Interrupts are a well known method of altering the processing flow in a digital data processor in response to an external event. For instance, in a microcomputer which is controlling the operation of an electromechanical system, a change of state of the system may require the generation of an interrupt request to trigger the microcomputer to alter its processing flow in order to perform some special function. The indication that a change of state has occurred is often in the form of information transmitted across one or more individual wires which is received at one or more pins of the microcomputer. Circuitry either external to or internal to the microcomputer then determines whether an interrupt request should be generated.
Some microcomputers today now allow the user to shut down a great deal of the electrical activity on the microcomputer chip, such as the clocks, in order to reduce power consumption when the microcomputer is not actively needed. The microcomputer is then "wakened" from this stop mode by an interrupt generated from either an internal stimulus or from a stimulus received at one or more external pins.